A. D. Albani

Palaeoenvironmental significance of a benthic foraminiferal fauna from an archaeological excavation in the Lagoon of Venice, Italy

Abstract An archaeological excavation at S. Francesco del Deserto Island in the Lagoon of Venice has revealed a lagoon sedimentary sequence containing the remains of a settlement from the 5th century. From this sequence, 11 samples were obtained and their foraminiferal content analysed. A statistical analysis of the relative foraminiferal abundance for different total counts has indicated that, even in palaeoenvironments, about 300 individuals form the optimal assemblage for a quantitative study. Cluster analysis applied to the optimal benthic assemblage has identified four foraminiferal biotopes in the sedimentary sequence. The foraminiferal faunas do not appear to be affected by post-depositional dissolution of the calcareous tests. A comparison with the present day faunas suggests that the site evolved from lagoonal conditions to salt marsh conditions. The salt marsh environment, which forms the base of the old settlement, is followed by another period of lagoonal conditions before forming the present day Island of S. Francesco. The presence of a salt marsh morphology, which defines the palaeo sea level, together with the paving of the 5th century settlement, indicates an average rate of subsidence of 1.37 mm/yr for the last 15 centuries.

Ancient and modern salt marshes in the Lagoon of Venice

Abstract The Lagoon of Venice was formed during the Late Holocene transgression and anthropogenic remains are common within its sedimentary sequences. This study is based on the foraminiferal association of 58 samples from 7 cores obtained from salt marshes north of Venice. Below horizons of lagoonal origin, these samples reveal the presence of faunas with Trochammina inflata (Montagu) and Helenina anderseni (Warren) which indicate conditions that are characteristic of present-day salt marshes. Foraminiferal faunas can identify the different lagoonal environments and indicate the relative position of the various horizons with respect to sea level. Faunas obtained from the lower section of the cores are analogous to present-day assemblages and they indicate, below a transgressive phase, the existence of buried ancient salt marshes occupied by human settlements. The absolute age of these horizons indicates that the establishment of human settlements is much older than previously thought and that the average rate of Holocene relative sea level rise for the last 5000 years is of the order of 1.2 mm/yr. The formation of these salt marshes, and their subsequent submergence, occurred with rates of accretion and subsidence markedly variable and with occasional erosional phases. This study also shows that, within the present lagoonal environment, together with erosional processes there are areas of accumulation with the formation of new salt marshes.

Benthonic foraminifera as indicators of intertidal environments

Recent benthonic foraminifera respond to even minor changes in environmental conditions. On the basis of statistical analyses of both foraminiferal population and bottom sediments, a new morphological terminology for the Lagoon of Venice is presented.The various geomorphic units are here differentiated on the basis of the relative occurrence of subpopulations that respond to local physicochemical and biological parameters. This reduces the need to evaluate the tolerance limits of each individual species, necessary to identify environments in terms of species or groups of species.

Preliminary estimate of the reservoir age in the Lagoon of Venice.

The Lagoon of Venice was formed about 6000 years ago due to the marine transgression associated with the late Pleistocene sea level rise. Already by the time of the Republic of Venice (727-1797 AD) it was recognized that the future of the city and its many historical buildings was strongly correlated with the future of the lagoon itself. During the centuries many engineering projects such as modification of the fluvial systems, construction of coastal barriers, and dredging of navigation channels were carried out to preserve the lagoonal environment. The present-day lagoon is the result of all these processes and covers an area of 540 km (super 2) with an average depth of 0.6 m. A series of radiocarbon age determinations carried out on material obtained from cores collected in the Lagoon of Venice indicate within the sedimentary units the existence of a number of discontinuities and slumping events due to the highly active lagoonal environment. The evaluation of data obtained from a variety of different materials--both terrestrial and marine--allowed us to determine for the first time the marine reservoir effect in the lagoon of Venice. The discussion includes a comparison with other relevant measurements and a possible explanation to the relatively high reservoir age (1200-1300 yr).

Resolution of foraminiferal biotopes in Broken Bay, N.S.W.

Abstract A recent benthonic foraminiferal population consisting of 144 species from an interacting marine‐estuarine environment has been analysed by Q‐mode cluster analysis to reveal biotopes. Simplification of the total populations, both in terms of abundance and occurrence, discloses that the more significant subpopulation is composed of the widely‐occurring species. Subpopulations based on rarely occurring but locally abundant species do not define meaningful biotopes.

The bedrock topography and origin of Broken Bay, N.S.W.

Abstract The bedrock topography of Broken Bay on the eastern coast of Australia has been investigated by means of a low‐power marine sparker system. It has been possible to reconstruct the upper Pleistocene drainage pattern, which differs somewhat from the present configuration of the estuary. Two distinct bedrock channels have been identified: the first along the present Hawkesbury River and the second along the present position of Pitt Water. They are separated by a rock bar across the entrance of Pitt Water. The Pitt Water channel has been identified as reaching the sea through the Palm Beach tombolo. Bedrock depths in the entrance of Broken Bay reach 125 m below sea level, which is consistent with the rise of sea level due to post‐glacial melting.

Biotopes of recent benthonic foraminifera in Pitt Water, broken Bay, N.S.W. (Australia)

Abstract Q-mode cluster analysis has been applied to a foraminiferal fauna from Pitt Water, N.S.W. (Australia), in order to define biotopes and their geographic extent. By successive elimination of the less commonly occurring species several biotope pattenrs have been obtained and mapped. These different sub-populations indicate that a large population has to be taken into consideration before cluster analysis can be successfully used. The biotopes determined show a meaningful relationship with the bottom topography and with the other environmental parameters.

Sedimentary environments in Broken Bay, N.S.W.

Abstract The recent sediments of Broken Bay (Australia) have been investigated to determine the environmental conditions prevailing in this estuary. Using Q‐mode cluster analysis of grainsize data four sedimentary environments have been defined and interpreted as of high and low energy of marine and fluvial origin. The behaviour of water masses as inferred from these four environments agrees with the hydrological data.

The geochemical anomalies in sediments on the shelf near the lagoon of Venice, Italy

Abstract Evaluation of the geochemistry of the bottom sediments on the shelf near the Venice Lagoon has revealed localized concentrations of the elements Cd, Cu, Ni, V, S, and, to a lesser extent, P. These elements are not known to be concentrated in the rocks within the catchment areas of the rivers that drain into the Lagoon and all distribution patterns indicate that they are not natural deposits. Pollution due to dumped smelter waste and residues from tanning and plating industries seems possible.

The bedrock topography of the botany basin, New South Wales

Abstract The bedrock topography of the Botany Basin has been determined from seismic‐sparker records made in Botany Bay and Bate Bay, and from seismic‐refraction and gravity measurements on the Kurnell Peninsula. Supplementary information has been obtained from boreholes both on land and in the sea. The Cooks and Georges Rivers formerly constituted the main drainage of the Basin and flowed generally southeastwards (beneath the present Kurnell Peninsula) and joined the Port Hacking River east of Cronulla. The depth of the bedrock channel of the former Georges River is 75–80 m b.s.l. at Taren Point, 90–95 m beneath the Kurnell Peninsula and 110–115 m at its junction with the Port Hacking River channel. The bedrock channel of the former Cooks River is about 30 m b.s.l. at Kyeemagh, its present entrance to Botany Bay, and it joined the Georges River at a location now 90 m b.s.l. beneath the Kurnell Peninsula. A second drainage system existed in the north and east of Botany Bay and generated the present mouth ...